This invention relates to counting apparatus arranged for the counting of the number of sheets in a stack thereof. In particular, the invention relates to such counting apparatus arranged to permit the insertion of a tab or marker between two sheets in the stack, after a pre-set number of sheets has been counted. The invention also relates to a method of tabbing sheets in a stack.
The counting apparatus of this invention is primarily intended to count sheets of paper, or paper-like materials, such as of plastics. Though the apparatus could be used to count other sheet-like materials, the invention will primarily be described with reference to the counting of sheets of paper either before or after printing, but it is to be understood that the invention is not limited to this use.
High speed sheet counters are already known, using a counting disc with at least one transfer slot (but usually several peripherally-spaced slots) from one face of the disc to the opposed disc face and through which sheets are transferred, one at a time. Each time a sheet is transferred, a count is incremented. The disc may count along a side edge of the stack of sheets or a corner region of that stack, depending upon the design. Examples of such counters are to be found for example in GB-1041049 and EP-0704079.
It is further known with sheet counters to insert a marker in the form of a short strip of paper or paper-like material, each time the count has incremented by a certain numberxe2x80x94for example, every one hundred sheets. The markers are usually referred to as tabs, and the apparatus for inserting the tabs, either a tab-inserter or a tabber, depending upon the precise configuration of the apparatus. Hereinafter, the term tabber will be used exclusively, to cover both forms of such apparatus.
On account of the thickness of the counting disc, the part of the stack which has already been counted is displaced from the remainder of the stack still to be counted, in the region of the disc itself. Known tabbers rely on there being a gap between these two parts of the stack in the region of but externally to the disc so that a tab may be projected into that gap at the required moment, just as the required count has been reached. Such a tabber is described in WO 96/07609.
Typically, for a disc counter which engages a corner region of the stack, a tab is inserted diagonally across the corner, in effect tangentially to the s counting disc. Such a tab is held relatively insecurely in the stack and often is repositioned manually after counting. In addition, the use of a tabber significantly reduces the maximum counting speed of a disc counter, if mis-tabbing is to be eliminated. In any event, paper-jams can occur should a tab, which is relatively flexible along its length, not slide smoothly between the required two sheets so that the tab then blocks subsequent counting or tabbing actions.
It is a principal aim of the present invention to improve on the known forms of tabber, to allow high speed counting of sheets of paper or paper-like materials, whilst at the same time permitting reliable tabbing whenever a required count has been achieved.
According to a first aspect of the present invention, there is provided counting apparatus for counting sheets in a stack thereof, which apparatus comprises a rotatable counting disc engageable with an edge region of the stack and including a sheet transfer slot to transfer the next sheet to be counted from one face of the disc to the opposed face on rotation of the disc, means to count the number of sheets transferred from one face to the other, advancing means to effect relative movement between the disc and the stack along the length of the stack as the sheets are counted, and a tabber arranged to insert a tab into the stack between two sheets when the count means achieves a predetermined sheet count value which tabber projects a tab in a generally radially-outward direction immediately adjacent one face of the disc and in a timed relationship to the rotation thereof, and the disc includes a tabbing recess in said one face and into which a projected tab is received for insertion between the last and next sheets to be counted at the moment of projection of the tab.
According to a second aspect of this invention, there is provided a method of tabbing sheets in a stack thereof using a rotatable counting disc engageable with an edge region of the stack and including a sheet transfer slot through which the next sheet to be counted is transferred from one face of the disc to the opposed face on rotation of the disc, the count being incremented each time a sheet is transferred from one face to the other and the disc being advanced along the length of the stack as the sheets are counted, in which method a tabber is arranged to insert a tab into the stack between two sheets when the count achieves a predetermined sheet count value which tabber projects a tab in a generally radially-outward direction with respect to the disc immediately adjacent one face of the disc and in a timed relationship to the rotation thereof, the tab being projected into a tabbing recess provided in said one face of the disc to be inserted between the last and next sheets to be counted at the moment of projection of the tab.
The tabber and method of this invention is fundamentally different from those of the prior art, in that a tab no longer is inserted into the gap created between the sheets by the presence of the disc, but external to the disc and in a generally tangential direction. Instead, a tab is projected in a generally radially outward direction with respect to the disc across the central region thereof. To permit the tab to move in that direction between the disc itself and the next adjacent sheet of paper, a recess is provided in the disc so as to define a space within which the tab may be moved. Such a space is positively defined by the disc, rather than by having to rely on the flexibility of the paper in the region of the periphery of the disc. Moreover, it is possible accurately to time the projection of a tab with respect to rotation of the disc, so the tab enters the recess. In turn, this greatly minimises the likelihood of mis-tabbing or a paper-jam, and so the maximum counting speed when employing tabbing may be increased, as compared to prior art tabbers.
Preferably, the tabbing recess is provided in the face of the disc which lies against the last sheet to be counted, following the transfer of that sheet through the transfer slot of the disc from the opposed face. Then, immediately after the counting of the nth sheet but before the picking-up of the (n+1)th sheet, the tab is projected into the recess so accurately marking the stack to show that there are n sheets on the counted paper side of the tab.
In order more positively to define the space into which a tab is projected and to minimise the likelihood of friction between a projected tab and the next sheet to be counted, it is preferred that there is a cover provided on the disc and which partially overlies the recess. Such a cover may be attached to the disc along the leading edge of the recess, having regard to the intended direction of rotation of the disc. By having the circumferential extent of the cover less than that of the recess, an exit slot is formed at the trailing edge of the cover for a projected tab, so as to leave the tab between the counted sheets and the next sheet to be counted, immediately before that sheet is transferred through the slot and counted. Alternatively, the circumferential extent of the cover may be greater than that of the recess, the trailing edge of the cover then being raised out of the general plane of the disc thereby to form an exit slot for a projected tab.
In addition, the radial extent of the cover preferably is less than that of the recess, with the radially outer edge of the cover spaced inwardly of the disc periphery. In this way, there will be both an entry slot for a tab being projected into the recess and a projection slot from that recess for a tab as it becomes fully projected so as then frictionally to engage between the last and next sheets to be counted.
In a preferred embodiment, the tab is projected at an acute angle to the general plane of the disc, against the counted-sheet surface of the discxe2x80x94said one face of the disc. The disc will then bend the tab round as the tab enters the recess, to be guided to lie between the sheets.
The disc advantageously has a plurality of transfer slots spaced therearound. In this case, there should be a tabbing recess in said one face of the disc between each pair of transfer slots. Thus, a tab may be inserted between any two sheets, whenever the count reaches the required value.
The tabber may include a source of tape for forming the tabs, such as a paper tape reel holder on which a reel of tape may be mounted, a tape drive mechanism and a guillotine arranged to cut from the tape a projected length thereof, following operation of said drive mechanism. Such a mechanism may comprise a pair of rolls defining a nip through which the tape passes and a drive arrangement for at least one of the rolls and operable to cause a length of tape to be projected in a timed relationship with respect to the rotation of the disc. Preferably, such a drive arrangement is adjustable to permit a tab accurately to be projected into a recess, despite different counting speeds. Such adjustment may be performed automatically, depending upon the counting speed.
In order to provide a timing signal for operation of the drive arrangement, a sensor may be associated with the disc and which provides a trigger output. For example, such a sensor may include an optical encoding disc together with a reader for that disc, which encoding disc is secured to the spindle supporting the counting disc. Alternatively operation of the tabber may be triggered by the required count signal, and in this case the sensor may simply provide a speed-sensing signal.
The counting apparatus of this invention could be arranged to engage either an edge region of a stack of sheets, partway along the length of a side of each sheet, or preferably a corner region of the stack. In one embodiment, there is provided a frame which supports the disc for rotation and means to hold a stack of sheets to be counted, the holding means being adapted to present to the disc the required part of the stackxe2x80x94and usually the corner region. One of the holding means or the disc should be arranged for movement relative to the other and the preferred arrangement is for the disc to be mounted for generally vertical movement while the stack remains stationary. The counting disc may be arranged to count from the bottom of the stack upwardly, with tabbing being performed as required during a counting operation. This has the advantage that the tabbing remnant (i.e. a number of sheets less than the number to be counted for each tabbing operation) will be at the top of the counted stack.